Worried about eating the right foods before a race or hard workout? Scientists at the University of Hull in England recently dialed in the perfect meal. They studied the effects of certain foods on the glycemic index to determine which would prove most beneficial when eaten pre-performance.

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The glycemic index (GI) is a scale of how carbohydrates affect our blood sugar. The index is based on the idea that not all sugars and carbs are equal. For example, a cookie and an apple can plausibly contain the same number of calories and grams of carbohydrates. But, a cookie can cause a blood-sugar spike and crash (leading you to an early bonk), while a lower-GI food like an apple provides sustained energy.

For the study, researchers compared the results of 40 km time trials ridden by cyclists eating high and low-GI foods. Forty-five minutes before the test, the cyclists ate cornflakes with low-fat milk (GI of 72) or branflakes with low-fat milk (GI of 30). The low-GI group finished the time trial on average three minutes faster than the high-GI group.

The stark advantage from the low-GI meal, explain the scientists, results because lower-GI foods lead to greater carbohydrate availability and usage during exercise. In other words, the athletes' food was more effective at providing fuel and that the fuel burned more efficiently. While the low-GI group was chugging away, the high-GI cyclists had to rely more of their fat reserves, which are harder for the body to burn than readily available carbs.

You can visit the University of Sydney's Glycemic Index Database and search for your favorite foods to find their scores. An index score of 55 is considered the line between high and low GI foods. For simple pre-race snacks, try apples, oranges, and dates. Among fruit, these have the lowest GI, with scores around 40.